The invention relates to a method as defined in the opening part of Claim 1.
The invention further relates to a communication device as defined in the opening part of claim 9.
The invention further relates to a transponder as defined in the opening part of claim 14.
The invention further relates to a circuit as defined in the opening part of claim 20.
A method as defined in the opening part of claim 1, a communication device as defined in the opening part of claim 9, a transponder as defined in the opening part of claim 14, and a circuit as defined in the opening part of claim 20 have been realized and put onto the market by the Applicant and are consequently known.
The known realizations are adapted to determine the characteristic values mentioned hereinafter, namely in the first place the value of the input capacitance of a transponder circuit existing between the input terminals of such a circuit and in the second place the value of the modulation index caused by load modulation means of a transponder circuit and appearing between circuit terminals of a such a circuit. In addition, the known realizations are also suitable for determining a correct digital functionality of a transponder circuit. With regard to the known realizations reference is also made to the European Patent Application having the application number 98 890 248.2 and filed on Aug. 21, 1998.
It is an object of the invention to adapt a method as defined in the opening part of claim 1, a communication device as defined in the opening part of claim 9, a transponder as defined in the opening part of claim 14, and a circuit as defined in the opening part of claim 20 in such a manner that it is possible to determine a characteristic value relating to the communication between a communication device and a transponder, which could not be determined hitherto, as a result of which a series of further possibilities of use are obtained for such a communication device, for such a transponder and for such a circuit.
According to the invention, in order to achieve the afore-mentioned object with a method as defined in the opening part of claim 1, the characteristic feature disclosed in the characterizing part of claim 1 has been provided.
Furthermore, according to the invention, in order to achieve the afore-mentioned object with a communication device as defined in the opening part of claim 9, the characteristic feature disclosed in the characterizing part of claim 9 has been provided.
Furthermore, according to the invention, in order to achieve the afore-mentioned object with a transponder as defined in the opening part of claim 14, the characteristic feature disclosed in the characterizing part of claim 14 has been provided.
Furthermore, according to the invention, in order to achieve the afore-mentioned object with a circuit as defined in the opening part of claim 20, the characteristic feature disclosed in the characterizing part of claim 20 has been provided.
As a result of the provision of the characteristic features in accordance with the invention it is achieved that now at least one time value can be determined which represents at least a part of the communication time interval in which a transponder has a communication connection with a communication device. In practice, this novel possibility in accordance with the invention provides a range of hitherto unrealizable potential uses. For example, in the case of an access control system formed by means of transponders and at least one communication device it is possible, by determining the at least one time value representing the communication time interval in which a transponder has a communication connection with a communication device, to determine when the transponder is in communication with the communication device during a communication time interval exceeding a given threshold value, which may be indicative of an operating fault or an unusual behavior of a user who carries the transponder, thus subsequently enabling an automatic failure indication or warning indication to be started and carried through. Further potential uses are obtained in all cases in which the communication time interval in which a transponder is in communication with a communication device plays a part.
It is to be borne in mind that the communication time interval is to be understood to means that time interval in which communication is possible between a transponder and a communication device, i.e. in which a transponder has a communication connection with a communication device, which is the case when the transponder is located within a communication range between the communication device and the transponder. In this respect it is to be noted that the communication range depends on the spatial position of the transponder with respect to the communication device. Moreover, it is to be noted that the duration of the method in accordance with the invention, for determining at least one time value representing at least a part of the communication time interval, preferably covers only a part of the length of the communication time interval.
For a method in accordance with the invention, a communication device in accordance with the invention, a transponder in accordance with the invention and a circuit in accordance with the invention it has proved to be particularly advantageous when, in addition, the characteristic features disclosed in claims 2, 10, 15 and 21, respectively are provided. By providing these characteristic features it is achieved in a simple manner that, in addition to at least one time value representing at least a part of a communication time interval, it is also possible to determine, without any additional expense, that a transponder or a circuit of a transponder no longer has a communication connection with a communication device, i.e. has left the communication range of a communication device.
In the above context it has proved to be particularly advantageous when, in addition, the characteristic features disclosed in claims 1, 9, 14 and 15, and 20 and 21, respectively are provided. By providing these characteristic features in accordance with the invention it is possible to determine at least one time value, which represents at least a part of the communication time interval which begins at a starting instant and which ends at an ending instant, in a particularly accurate manner.
In the above context it has proved to be very advantageous when, in addition, the characteristic features disclosed in claims 2, 10, 16 and 22, respectively are provided. This is particularly advantageous because such a counting stage provided as time-value determining stage can be realized simply in digital form.
However, it is to be noted that a time-value determining stage can also be realized at least partly in digital form, for example by means of a capacitor which can be charged with the aid of a charging circuit during a communication time interval, as a result of which the capacitor voltage appearing at a given instant within the communication time interval always forms a measure of a part of the communication time interval, i.e. a time value.
In connection with the determination of a time value which represents a communication time interval which begins at a starting instant and which ends at an ending instant, it has also proved to be advantageous when, in addition, the characteristic features disclosed in claims 5, 11, 17 and 18, and 23 and 24, respectively are provided. Such an embodiment is advantageous because in such an embodiment the desired result is accomplished by means which are present anyway, which in particular resides in the fact that the presence detection means and the absence detection means are formed by a so-termed power-on reset circuit which is present anyway in each circuit for a transponder.
In the above context it has also proved to be very advantageous when, in addition, the characteristic features disclosed in claims 6, 12, 19 and 25, respectively are provided. In the present case the advantage also resides in the fact that such a counting stage can be realized simply in digital form.
Furthermore, owing to the provision of these characteristic features in accordance with the invention it is possible in a simple manner and substantially without any additional means to calculate the physical time interval corresponding to a determined time value, i.e. to a numerical value determined as the time value, for example to enable this time interval to be displayed, which may be advantageous for monitoring purposes.
Furthermore, owing to the provision of these characteristic features in accordance with the invention it is possible in a simple manner and substantially without any additional means to determine the position where a transponder is located in relation to a communication device. Such a position determination is of great advantage, for example in conjunction with conveyor belts for items of luggage which each have an associated transponder included in an identification loop, because in this way the position of successive items of luggage carried by a conveyor belt can be determined very accurately in a simple manner.
Furthermore, this guarantees that in the case, which occurs very often in practice, that a plurality of transponders communicate simultaneously with a communication device, each of these transponders can be identified unambiguously and, consequently, at least one time value representing at least a part of the communication time interval of each respective transponder can be determined.
The afore-mentioned as well as further aspects of the invention will become apparent from the embodiments described hereinafter by way of example and will be elucidated with reference to these embodiments.